Enhancement on energy extraction from magnetic energy harvesters

This paper presents a method for enhancing performance of a magnetic energy harvester. The harvester operates with a magnetically saturating core with high magnetic permeability. If the core saturates, the effective magnetizing inductance becomes small, and little power can be harvested from the core. Energy is harvested very efficiently during an operating cycle when the core is not saturated, a time period we call the “transfer window.” It can be shown that the location and the length of a transfer window are independent of each other. Based on this property, the transfer window alignment (TWA) method is introduced for maximizing power harvest. The TWA method manipulates the location of the time window, and harvests a greater amount of power compared to passive rectification. The principle of the TWA method reveals that deeper core saturation with higher voltage stress leads to a higher level of energy extraction. The analysis of the TWA method is presented, and verified with simulation and experiments. A detailed control sequence for actual implementation is presented. The TWA method poses little burden to hardware complexity.